- Publish Date
- Sunday, 17 June 2018, 8:07AM
The 14-year-old star is on crutches and showed off a brace on her leg, but didn't explain how she'd sustained the injury in a video she shared to Instagram.
The 'Stranger Things' actress has been ordered to "rest up" so her injury means she will be unable to attend the MTV Movie & TV Awards on Monday (18.06.18).
She said in the clip: "Another milestone in my life, I've never actually broken a bone.
"I have split my knee cap so from the doctor's orders, he told me to rest up and that means I won't be attending the MTV Awards."
The teenager went on to express her wish that her co-stars have the "best time" at the glamorous event.
She added: "I hope that Finn, Gaten, Caleb, Sadie and Noah have the best time. I love them so dearly and I wish them the best, and I'm sending my luck with you. I'll be there in spirit.
Last year, Millie - who recently quit Twitter over homophobic memes featuring her photo - picked up the Best Actor in a Show award at the MTV Movie & TV Awards and she's up for the same accolade this year, as well as Best Kiss.
Meanwhile, Millie has become known for her kind deeds, as she previously vowed to attend the birthday party of 12-year-old fan Aaron, after he threw a party based on 'Stranger Things' only to find that none of his friends showed up.
Aaron's sad news was shared on Twitter by his older sister, and Millie - who plays Eleven - replied: "What!!!! Oh Well, You can let them all know that everyone on behalf of Stranger things would've come! I think your awesome and next year I would like an invite... Please? (sic)"